(Not Applicable)
The present invention relates generally to protective coatings and methods of forming protective coatings on a substrate. In particular, the present invention is directed to a liquid crystal polymer formed on a substrate to protect the substrate from the environment.
As is well known, metallic and composite structures mounted upon the exterior of ships, aircraft, and other objects subject to the environment can experience significant degradation and damage due to their exposure to erosion-corrosion attack. In this regard, such structures are constantly subjected to oxidation, moisture, erosion, fouling, salt spray, wear, ultraviolet radiation, impact, high/low temperatures, and chemicals, among other things, that can cause such structures to experience significant degradation and damage over time. As a consequence, such structural components must be constantly repaired or replaced to thus prevent the possibility that a given vessel or aircraft will be damaged permanently, if not destroyed.
In an attempt to prevent damage to a substrate caused by its exposure to the environment, a variety of coating agents and methods of applying the same to such components have been developed to improve the durability of the substrate and coating. To this end, liquid crystal polymer coatings (LCP coatings) have been utilized. In this regard, LCPs have been coated on substrates via spraying. However, merely spraying LCPs onto a substrate without preheating the substrate to maintain the liquid crystal polymer in a plastic state upon contact thereon will form a LCP coating with voids contained therein. Additionally, merely spraying LCPs onto a substrate without preheating the substrate to maintain the liquid crystal polymer in a plastic state upon contact thereon will reduce the adhesion between the substrate and the LCP coating. In relation to the voids, the same reduces the effectiveness of the coatings barrier properties. Additionally, the voids behave as starting points for cracks that may propagate due to foreign object impact from the environment. As such, voids in the layer of liquid crystal polymer reduce the life of the protective coating.
Another method of applying a liquid crystal polymer is to bond a film of the polymer onto the substrate. However, in general, the liquid crystal polymer film is not useful for bonding onto contoured surfaces because the film is not stretchable. Furthermore, film form of liquid crystal polymers have long chain molecules in orderly arrangement.
In an embodiment of the present invention, a protective layer is provided for protecting a substrate from an environment. The protective layer comprises an aggregate of long chain molecules wherein each long chain molecule is randomly oriented and consistently entangled to adjacent long chain molecules throughout the aggregate of long chain molecules. The aggregate of long chain molecules is essentially free from voids. The aggregate of long chain molecules is essentially free from residual stresses. The long chain molecule is a liquid crystal polymer. The protective layer is disposed on the substrate.
In another embodiment of the present invention, a method of forming a protective layer on a substrate is provided to protect the substrate from an environment. The method comprises 1) disposing an aggregate of long chain molecules in a liquid state onto the substrate such that each long chain molecule is randomly oriented, 2) maintaining the liquid state of the aggregate of long chain molecules such that each long chain molecule is consistently entangled to adjacent long chain molecules throughout the aggregate of long chain molecules, and 3) solidifying the aggregate of long chain molecules from the liquid state to a solid state.
The method may further comprise a pre-heating step which injects heat into the aggregate of long chain molecules prior to the disposing step to facilitate consistent entanglement of each long chain molecule to adjacent long chain molecules throughout the aggregate of long chain molecules.
In relation to the disposing or the maintaining step, those steps may further include the step of injecting heat into the aggregate of long chain molecules.
During the injecting heat step, such step injects heat into the aggregate of long chain molecules at a plurality of sites which are independently controllable with respect to each other. The amount of heat to be injected at each site is in response to a sensed temperature of the aggregate of long chain molecules. Additionally or alternatively, the heat being injected into the aggregate of long chain molecules at the sites may be in response to a compared deviation between the sensed temperature and a stored temperature. The sensed temperature may be obtained with an optical pyrometer.
The heat may be injected into the aggregate of long chain molecules through an environmentally exposed side of the aggregate of long chain molecules. By way of example and not limitation, the heat may be injected through conduction, convection, thermal radiation, or combinations thereof.
Additionally, in relation to the disposing step, such step may be accomplished by spraying droplets onto the substrate wherein each droplet is a portion of the aggregate of long chain molecules. The droplets have a diameter of about 20 microns to about 80 microns. Preferably, the diameter of the droplets are about 50 microns to about 60 microns. The spraying of the droplets may be accomplished with a mechanically controlled spray gun traversing the substrate at a selected spray distance and traverse rate. By way of example and not limitation, the spray gun may be a thermal spray plasma, combustion, or high velocity oxi fuel gun.
In relation to the maintaining step, such step is performed until the aggregate of long chain molecules are essentially free from residual stress.